Risk factors for lungworm-associated milk yield losses in grazing dairy cattle.

Dictyocaulus viviparus, the causative agent of bovine parasitic bronchitis, is an important parasite of dairy cattle. Infections can lead to substantial economic losses, due to mortality, reduced weight gain and milk production and treatment costs. There have been relatively few studies investigating herd management risk factors for infections with D. viviparus and lungworm-associated production losses. The aims of this study were (1) to assess the impact of (sub)clinical lungworm infections on productivity in dairy cows and, (2) to identify or confirm risk factors, related to herd management, for infections in grazing dairy cattle. Using a recombinant Major Sperm Protein (MSP)-based ELISA, the presence of D. viviparus antibodies in bulk tank milk (BTM) samples was evaluated on 717 and 634 farms at two-week intervals during two grazing seasons (2018 and 2019). Associations between milk antibody levels and production data (mean milk yield in kg/cow/day, percentage of fat and protein) were assessed, as well as associations with putative risk factors in the herd management, gathered through a questionnaire survey. In both years, there was a substantial, but non-significant, difference in the annual mean milk yield on farms with at least one BTM sample above the cut-off of 0.41 ODR, compared with the mean milk yield on farms that stayed under this threshold on each sampling day (-0.17 and -0.70 kg milk/cow/day in 2018 and 2019, respectively). In 2019, this association was stronger, and significant, when the cut-off was exceeded in at least two consecutive BTM samples (-1.74 kg milk/cow/day). BTM results were also significantly negatively associated with the closest milk production data during the two-weekly BTM sampling intervals in 2019. A single or two consecutive positive tests were used in the risk factor analysis as a proxy for lungworm-associated milk yield losses. Purchase of new animals (Odds Ratio (OR) = 2.68) and the proportion of the first grazing season covered by preventive anthelmintic treatment (OR up to 3.88, depending on proportion) were positively associated with lungworm-associated milk yield losses, while mowing at least 50 % of the pastures (OR = 0.57) was negatively associated with lungworm-associated milk yield losses. Our results suggest that the ELISA holds promise to identify herds with significant production losses due to lungworm infections, under the condition that BTM sampling is done repeatedly during the grazing season. Based on the confirmed risk factors, adjustments of the farm management could perhaps mitigate these losses.

Pathological lesions in the lungs of red deer Cervus elaphus (L.) induced by a newly-described Dictyocaulus cervi (Nematoda: Trichostrongyloidea).

The large lungworms of the genus Dictyocaulus are causative agents of parasitic bronchitis in various ungulate hosts, including red deer. Recently, the red deer-derived lungworm D. cervi was described and separated from D. eckerti. Little is known of the transmission patterns, epidemiology, geographical distribution and pathogenicity of D. cervi. Histological examinations were performed on 22 formalin-fixed lung tissue samples of hunted red deer. Exclusively, D. cervi adults were derived from 15 red deer and confirmed molecularly (GenBank accession: MH183394). Dictyocaulus cervi infection was associated with various degrees of lung pathology, including interstitial pneumonia, bronchitis and bronchiolitis with an influx of eosinophils, lymphocytes, plasma cells and macrophages; massive hyperplasia of lymphoid follicles within bronchiolar tissue, and hyperplasia of the bronchial and bronchiolar epithelium. Furthermore, emphysema, atelectasis and lung tissue congestion were noted. Interestingly, interstitial and subpleural fibrosis was seen in adult Dictyocaulus-negative samples, suggesting either a prepatent phase of Dictyocaulus infection or infection/coinfection with protostrongylid nematodes.

The effect of patent Dictyocaulus viviparus (re)infections on individual milk yield and milk quality in pastured dairy cows and correlation with clinical signs.

BACKGROUND: Infections with the bovine lungworm Dictyocaulus viviparus might lead to reduced milk production and detrimental impacts on milk quality resulting in considerable economic losses in dairy farming. METHODS: In the presented field study, 1988 faecal samples were collected from 1166 Black and White dairy cows allocated in 17 small and medium-sized German grassland farms. Faecal samples were collected in summer and autumn 2015 to assess D. viviparus larvae excretion. Test-day records were used to estimate the association between patent D. viviparus infections in individual cows and the milk production parameters milk yield, milk protein and milk fat content by using linear mixed models. Bulk tank milk (BTM) samples from each farm and individual milk samples from those cows which were excreting larvae in summer were collected in autumn. In addition, occurrence of the clinical symptom "coughing" was noted in individual cows during autumn sampling to determine its association with patent lungworm infections. RESULTS: Patent D. viviparus infections were found on 23.5% (4/17) of farms with a prevalence at the individual cow level of 0.9% (9/960) in summer and 3.4% (35/1028) in autumn. No BTM sample exceeded the BTM ELISA cut-off value of 0.410 optical density ratio (ODR), the mean value was 0.168 ODR. Only one individual milk sample exceeded the individual milk ELISA cut-off value of 0.573 ODR (mean value of 0.302 ODR). A patent D. viviparus infection status was associated with a lower average daily milk yield of 1.62 kg/cow/day (P = 0.0406). No significant association was found with milk protein or fat content representing milk quality parameters. Coughing was observed in 5.9% (61/1028) of cows. Of the coughing cows, only 4.9% (3/61) had a patent lungworm infection. Fisher's exact test showed no significant difference between infected and non-infected coughing cows. CONCLUSIONS: Farmers and veterinarians should be aware that patent lungworm (re)infections in dairy cows reduce milk yield, despite the absence of clinical signs. Furthermore, if dairy cows present with coughing, other differential diagnoses need to be considered in addition to dictyocaulosis.

Oxidative stress in dairy cows naturally infected with the lungworm Dictyocaulus viviparus (Nematoda: Trichostrongyloidea).

The aim of this study was to analyse the oxidative and anti-oxidant status in serum samples from dairy cows naturally infected by Dictyocaulus viviparus and its relation with pathological analyses. The diagnosis of the disease was confirmed by necropsy of one dairy cow with heavy infection by the parasite in the lungs and bronchi. Later, blood and faeces were collected from another 22 cows from the same farm to measure reactive oxygen species (ROS) levels, thiobarbituric acid-reactive substances (TBARS), catalase (CAT) and superoxide dismutase (SOD) activities on day 0 (pre-treatment) and day 10 (post-treatment with eprinomectin). Faecal examination confirmed the infection in all lactating cows. However, the number of D. viviparus larvae per gram of faeces varied between animals. Cows showed different degrees of severity according to respiratory clinical signs of the disease (cough and nasal secretion). Further, they were classified and divided into two groups: those with mild (n = 10) and severe disease (n = 12). Increased levels of TBARS (P < 0.001), ROS (P = 0.002) and SOD activity (P < 0.001), as well as reduced CAT activity (P < 0.001) were observed in cows with severe clinical signs of the disease compared to those with mild clinical signs. Eprinomectin treatment (day 10) caused a reduction of ROS levels (P = 0.006) and SOD activity (P < 0.001), and an increase of CAT activity (P = 0.05) compared to day 0 (pre-treatment). TBARS levels did not differ with treatment (P = 0.11). In summary, increased ROS production and lipid peroxidation altered CAT and SOD activities, as an adaptive response against D. viviparus infection, contributing to the occurrence of oxidative stress and severity of the disease. Treatment with eprinomectin eliminated the infection, and thus minimized oxidative stress in dairy cows.

Antibodies against Dictyocaulus viviparus major sperm protein in bulk tank milk: Association with clinical appearance, herd management and milk production.

The objective of this study was to conduct a comprehensive field survey using a Dictyocaulus viviparus major sperm protein ELISA on bulk tank milk samples from Belgian dairy herds to gain insights in: (1) the sensitivity (Se) and specificity (Sp) of the test under field conditions; (2) the value of the test to predict a future clinical lungworm outbreak; (3) its associations with milk production parameters and (4) its associations with herd management factors. A total of 1248 herds were sampled, with samplings occurring in the middle ("August") and towards the end ("October") of the grazing season. A completed questionnaire on potential risk factors and potentially lungworm-induced clinical signs was obtained from 587 farms and milk production records could be obtained from 343 herds. The median (25th-75th percentile) D. viviparus antibody level (ODR) was 0.25 (0.19-0.31) in "August" and 0.24 (0.19-0.32) in "October". At a threshold of 0.41 ODR, the Se and Sp were estimated using mixture models at 50 and 99%, respectively. At the same threshold, the positive and negative predictive value of the ELISA applied in "August" on the occurrence of farmer-reported lungworm symptoms in the period August-November were 65% and 69%, respectively. D. viviparus antibody levels were significantly higher in the north vs. the south of the country, in large herds and in herds that did not mow pastures or that frequently purchased new animals. An increase in the ELISA result of "August" over the interquartile range was associated with a drop in the annual average milk yield, milk protein% and milk fat% of -0.50kgcow-1day-1, 0.02 and 0.02, respectively. The relationships between the ELISA results in "October" and milk production parameters were also negative, but lower and non- or only marginally significant. We conclude that the bulk tank milk ELISA has a low value to predict lungworm disease on an individual farm based on a fixed sampling date in the middle of the grazing season. On the other hand, the test has been potential to detect subclinical production impacts and study risk factors through epidemiological surveys.

Susceptibility of elk to lungworms from cattle.

Two studies were conducted to determine the infectivity of the lungworm, (Dictyocaulus viviparus) of cattle origin, in Rocky Mountain elk (Cervus elaphus nelsoni) or wapiti. In the first study, each of three 9-mo-old elk was administered 3,000 D. viviparus larvae from cattle using a nasogastric tube. In the second study, four 16-mo-old elk were each inoculated with 2,000 D. viviparus from cattle using a nasogastric tube. Elk were observed daily for signs of respiratory disease, and fecal samples were collected during the studies and evaluated for lungworm larvae using a modified Baermann technique. One elk was euthanatized during the patent period for recovery of adult lungworms, and three elk were euthanatized after larvae were no longer detected in feces. Lungworm larvae were not detected before inoculation in any of the 16-mo-old elk, but were detected 22 days after inoculation in one elk, 23 days after inoculation in two elk and 24 days after inoculation in all four elk. The prepatent period of this cattle isolate of D. viviparus in elk is therefore 22 to 24 days. The precise prepatent period was not determined in the three 9-mo-old elk, but larvae were detected in all three elk 25 days after inoculation. Numbers of larvae ranged from 1/ to 101/g feces with peak larval detection occurring 32 to 50 days after inoculation. Elk shed larvae from 22 to 83 days after inoculation, and patent periods of the parasite ranged from 24 to 62 days. Clinical signs of respiratory disease, with the exception of mild coughing after exercise, were not observed during the infections. Results from this experiment indicated that D. viviparus larvae of cattle origin can mature in elk and larvae can be passed in large numbers in feces, but this cattle isolate of D. viviparus was not highly pathogenic in elk.

Weight gain of calves during natural lungworm challenge infection is non-linearly related to previous infection history.

Calves, previously subjected to different rates of artificial lungworm infection for 10 weeks, were challenged with a natural lungworm infection on pasture after a 6-week housing period. The results showed a parabolic relationship between the effect of the natural challenge on weight gain and the previous rate of artificial infection. The highest average daily weight gains were observed in the calves previously subjected to intermediate rates of artificial infection. The results suggest the existence of an optimal rate of initial infection at which there is sufficient development of immunity to resist the pathogenic effects of reinfection without a concomitant penalty on weight gain.

An experimental field study on the build up of lungworm infections in cattle.

The build up of lungworm infections was studied in four groups of calves. Calves of Group 1 were infected experimentally with 6 x 10 larvae during the first 3 weeks after turnout. The pasture of Group 2 was contaminated with approximately 35,000 larvae in June and the pasture of Group 3 with approximately 1.3 million larvae in August. Group 4 served as the helminth free control group for challenge infections with 5,000 larvae in October. In Group 1 faecal larval counts increased 5 weeks after the beginning of patency and decreased after another 3 weeks, indicating the development of immunity after the second lungworm generation. In contrast, the development of immunity in Groups 2 and 3 occurred after the first lungworm generation as maximal faecal larval counts were seen within 3.5 weeks after the beginning of patency. Infection levels were highest in Group 3 which was the only group showing clinical signs. These signs became worse after oxfendazole treatment.

Globule leukocytes and bovine parasitic bronchitis.

Globule leucocytes (GL) occur in the respiratory tract of cattle from foetuses to adult animals. Large numbers of this cell have been found in the lungs of cows both in normal lung and in the lungs of cows from various outbreaks of respiratory diseases, but the significance was not known. In the rat and in cattle, the occurrence of GL in the gastrointestinal and urinary tracts has been associated with parasitic infections. The relationship between the respiratory tract GL and Dictyocaulus viviparus infections in cattle was studied in three groups of parasite free calves experimentally infected with D. viviparus. Group 1 animals received single challenge infections. Group 2 had three subgroups (2a, 2b, 2c) which were either vaccinated and challenged (2a), given a single challenge (2b) or used as vaccinated controls (2c). Group 3 with four subgroups (3a, 3b, 3c, 3d) were either used as environmental controls (3a), vaccinated and repeatedly challenged (3b), given normal larvae of D. viviparus and repeatedly challenged (3c) or as a trickled group 3d. Although GL were found in infected calves, it was not possible to demonstrate a clear cut correlation between their presence or density and the method of exposure.

Morphological investigations on the pathology of Dictyocaulus viviparus infections in cattle.

Morphological investigations of lungs obtained from cattle that had been experimentally infected with Dictyocaulus viviparus were carried out using a new fixation technique that excludes post-mortem changes in the samples. Light and electron microscopical investigation showed a substantial loss of ciliated epithelial cells in the bronchi, severely affecting the mucociliary clearance. Bronchiolitis, peribronchiolitis and cell-rich mucus caused bronchial atelectasis and consolidation of the related alveoli. Interlobular septa completely separated diseased from normal tissue. Clara cells contained abundant intraplasmatic glycogen. Alveolary walls were thickened and showed cellular infiltration, loss of functional epithelial cells and hyperplasia of alveolar type II cells. Increased connective tissue indicated an irreversible chronic decline in lung performance. Lung eosinophilia and the cytotoxic abilities of eosinophils are discussed as a cause of the changes in lung tissue after infection with D. viviparus.

Immunity to parasitic bronchitis of yearling cattle treated with ivermectin during their first grazing season.

A group of 12 winter-born calves was divided into two groups of six. During the following summer one group grazed on pasture infected with Dictyocaulus viviparus, and was treated with ivermectin injections at three, eight and 13 weeks after turn out. The other group remained housed. Both groups were housed during the winter and then together with a group of younger calves were challenged with a trickle infection of D viviparus larvae at the rate of 25 third stage larvae/kg bodyweight for one month and then slaughtered. The group which had been exposed to previous infection was least affected by parasitic bronchitis and on the basis of serological titres and worm burdens had developed resistance to the challenge infection. The other older group was also more resistant than the younger calves.

Clinical signs following experimental lungworm infection and natural bovine respiratory syncytial virus infection in calves.

Similar clinical signs have been reported in calves infected either by Dictyocaulus viviparus or bovine respiratory syncytial virus. Three experiments were carried out to establish the clinical picture and the course of the disease in animals with these infections. The clinical signs of calves infected with lungworm included coughing, nasal discharge, tachypnoea, abdominal breathing and pyrexia, and auscultation of their lungs revealed increased bronchial sounds. Similar signs were also observed after infection with bovine respiratory syncytial virus, but the signs were more acute and resolved more rapidly than in animals infected with lungworm larvae. Calves infected with lungworm had more serious clinical signs after infection with bovine respiratory syncytial virus than calves, which were not infected with lungworm.

Serum lactate dehydrogenase: clinical significance of alterations in its activity in lambs infected with Dictyocaulus filaria.

Alterations in the serum lactate dehydrogenase activity of Dictyocaulus filaria infected lambs were studied. The significant increase in its activity during patency correlated well with the progress of the disease and lung damage caused by the parasite. The enzyme may be of use in assessing the potency of D filaria vaccine and the chemotherapeutic value of an anthelmintic. Its use as a non-invasive method for earlier diagnosis and prognosis of the disease under experimental conditions is suggested.

Parasitic bronchitis and pneumonia.

Parasitic bronchitis and pneumonia is often a serious problem on individual farms, despite the fact that the disease is easy to diagnose, easy to treat, and easy to prevent by anthelminthic control programs or by vaccination. This article presents the various phases of the primary infection as well as the reinfection syndrome.

Histopathological findings in the lungs of Scottish red and roe deer.

Histopathology on portions of lung collected from 34 red deer (Cervus elaphus) and 15 roe deer (Capreolus capreolus) between 1977 and 1981 revealed evidence of lungworm infestation in 16 red and 14 roe deer. In the red deer, Dictyocaulus species, and the developmental stages of another parasite, believed to be Elaphostrongylus cervi, were involved. Dictyocaulus also affected the roe deer, but in them the major lesions were associated with protostrongylids. Exudative bronchopneumonia, including two cases of fungal infection, was predominantly a problem of red deer under seven months of age. Between the age of four and seven months, parasites frequently accompanied this change. Other conditions encountered were pulmonary congestion, tuberculosis and granulomata of unknown cause.